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  <head>
    <meta charset="UTF-8" />
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    <title>Document</title>
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  <body>
    <script>
      //需求：求1-100偶数和
      var i = 2,
        sum = 0;
      while (i <= 100) {
        sum += i;
        i += 2;
      }
      document.write("1-100偶数和为:" + sum);
    </script>
  </body>
</html>
